Slope=rise/run we see that the slope will be negative it is more accurate the farther we are apart we wiill use the points closest to the line, those are (3.5,3.5) and (5,1)
slope between (x1,y1) and (x2,y2) is (y2-y1)/(x2-x1) for this one (1-3.5)/(5-3.5)=-2.5/1.5=-1.666666666≈-1.67